This study is designed to further investigations of adaptive changes in skeletal muscle tissue associated with alterations in muscle length. Alterations in muscle length occur normally during growth, but also can be induced by modifications of the intermaxillary space and by orthognathic surgical procedures. Our primary objective is to broaden our understanding of the structure and function of the muscles of the craniofacial musculature resulting from alterations in resting length, and/or from muscle detachment. Specific structural and functional adaptations will be produced and investigated by histochemical, biochemical, anatomical and physiological techniques, which we have used previously in studies of craniofacial adaptation. Data and interpretations gained from this study will be combined with data gained from our previous experimental investigations, leading to a better understanding of musculoskeletal adaptations in the craniofacial region.